In this study, airborne electromagnetics (AEM), high resolution LiDAR, and drilling (100 bores) were acquired to map and assess groundwater resources and managed aquifer recharge options in the River Darling Floodplain. Neotectonic faulting and uplift has previously been described along the north-western margin of the Murray Basin along the adjacent Darling Lineament, however no evidence of neotectonics had previously been identified in the study area. Initial inversions of the AEM data revealed a multi-layered conductivity structure broadly consistent with the hydrostratigraphy identified in drilling. However, initial laterally and spatially constrained inversions showed only moderate correlations with ground data in the near-surface (∼20m). As additional information from drilling and ground and borehole geophysical surveys became available, various horizontal and vertical constraints were trialled using a new Wave Number Domain Approximate Inversion procedure with a 1D multi-layer model and constraints in 3D. The resultant 3D conductivity model revealed that an important Pleistocene aquitard (Blanchetown Clay) confining the main aquifer of interest (Calivil Formation), has an undulating surface, which is locally sharply offset. An interpreted top surface suggests that it has been affected by significant warping and faulting, as well as regional tilting due to basin subsidence or margin uplift. Overall, the top surface of the Blanchetown Clay varies in elevation by 60m. Many of the sharp offsets in the conductivity layers are coincident with lineaments observed in the LiDAR data, and with underlying basement faults mapped from airborne magnetic data. The identification of neotectonics in this area was made possible through the acquisition of high resolution AEM data, and the selection of appropriate horizontal and vertical constraints in inversion procedures. Recognition of faulting in the unconsolidated sedimentary sequence helps explain the rapid recharge of underlying Pliocene aquifers, with neotectonics recognised as a key component of the hydrogeological conceptual model.
The East Kimberley Region of north-western Australia has been identified as a priority for potential agricultural development. Within this region, the Ord Bonaparte Plain is remote, with limited access in an area of great cultural and environmental sensitivity. Initially, spatio-temporal mapping using remote sensing (and potential field) data, combined with data on the deeper basin geology was used to plan an airborne electromagnetics (AEM) survey. The relatively resistive nature of the basin sediments has enabled the AEM to map the hydrostratigraphy to depths of 300-500m, except in the coastal zone affected by seawater intrusion. Two overlying aquifers, separated by a faulted, ‘leaky’ aquitard, have been identified.The AEM and remote sensing data were subsequently used to plan a ground magnetic resonance (GMR) survey. The latter has enabled a water table map to be constructed in an area with almost no drilling, while also enabling key aquifer properties to be determined. The target aquifer has a high free water content and high transmissivity. The GMR results have been validated by drilling, borehole Nuclear Magnetic Resonance (NMR), and induction logging.Integration of AEM, GMR and temporal (Landsat) remote sensing data has enabled rapid mapping and characterisation of the groundwater system in a data-poor, culturally and environmentally sensitive area. These data have also revealed complex faulting within and bounding the aquifer system, delineated the sea-water intrusion interface, and mapped groundwater dependent ecosystems. These data have been used to target drilling and pump testing that will inform groundwater modelling, water allocations and development decisions.
Over the past decade, advances in new satellite and airborne sensor technologies provide an opportunity for rapid multi-scale mapping, measurement and monitoring of the physical state of the crust, including resolution of key elements of surface and sub-surface hydrological systems. These advances have been mirrored by the development in advanced computational research infrastructure which is now giving the groundwater research community access to high-resolution (spatial and temporal) biophysical datasets (e.g. climate, ecology, geoscience and geospatial) relevant to broader hydrological systems understanding. This infrastructure facilitates integration of multiple datasets and rapid and improved signal processing, inversion, and sophisticated analysis. These datasets provide a catalyst for collaboration, with inter-disciplinary approaches enabling new discovery science in a ‘big data’ environment, and enabling the qualitative and quantitative analysis and modelling of landscape and hydrological system processes.In Australian landscapes, airborne electromagnetics (AEM) is widely used in near-surface (<200m) groundwater investigations due to the ability to acquire consistent, spatially coherent information of high quality using calibrated systems, in very short timeframes. This study reports on an evolving inter-disciplinary approach to AEM survey design for groundwater exploration. Recent investigations have employed time series analysis of surface water availability (using the Australian Geoscience Data Cube (AGDC)) combined with morphotectonic analysis of digital elevation datasets, tectonic analysis, and geomorphic analysis of satellite optical data, to help predict preferential recharge zones and shallow groundwater resources. This novel approach has been used successfully for groundwater exploration in the western Murray Basin and Kimberley Region of northern Australia.
This study uses FDHEM data collected from the Riverland South Australian Salinity Mapping and Management Projects, using the RESOLVE system. The Riverland survey was collected along the southern floodplains near Loxton, South Australia, an area of largest salt export along the Murray River. The objective of the Riverland survey was to map the depth, thickness and conductivity of two layers, the Blanchetown Clay and the saline groundwater. Definition of useful targets for the AEM survey, rather than a simplistic salinity mapping approach, was undertaken to provide the level of detail and understanding required. Survey design based on knowledge of the hydrogeological framework and pre-survey down-hole induction conductivity logging enabled forward modelling of the likely EM response of the target given a particular airborne EM system and survey parameters. Further to this, use of a priori knowledge of the local geomorphic and geological landscapes, density of boreholes and other geophysical information was investigated in the context of survey planning of line and tie line density. Initial line spacings were derived from a model describing the smallest target of interest in the survey, 150 metre diameter holes in the Blanchetown Clays, so that at least two lines would intersect the smallest target.
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
